Oxidation protected separator

ABSTRACT

A battery separator for a lead/acid battery is resistant to oxidation arising from the use of water or acid containing contaminants, for example chromium (Cr), manganese (Mn), titanium (Ti), copper (Cu), and the like. The separator is a microporous membrane including a rubber. The rubber is no more than about 12% by weight of the separator. The rubber may be rubber latex, tire crumb, and combinations thereof. The rubber may be impregnated into the microporous membrane. The microporous membrane may be a microporous sheet of polyolefin, polyvinyl chloride, phenol-formaldehyde resins, cross-linked rubber, or nonwoven fibers. A method for preventing the oxidation and/or extending battery life of the separator is also included.

RELATED APPLICATION

This application claims the benefit of U.S. provisional application No.61/774,160 filed Mar. 7, 2013, incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed to a battery separator for lead/acidbatteries being resistant to oxidation arising from the use of waterand/or acid containing contaminants.

BACKGROUND

Oxidation of the separator, e.g., separators for lead/acid batteries,reduces a battery's cycle life, and thereby reduces the effective lifeof the battery. Oxidation causes the embrittlement (measured by, forexample, loss of % elongation) of the separator which leads to partialor complete failure of the battery.

Contaminants typically originate from the water and/or the sulfuric acidadded to a battery, as well as from impurities in the alloys and activematerials that comprise the electrode plates, may cause oxidation. Suchcontaminants typically include the transition metals of the periodictable, for example: chromium (Cr), manganese (Mn), titanium (Ti), copper(Cu), and the like. Contaminant levels (e.g., Cr, Mn, and/or Ti) ofgreater than about 2.0 ppm [2.0 mg/L] are not recommended. Cucontaminants greater than 26 ppm [26 mg/L] are not recommended. Inbatteries without contaminants (e.g., Cr), the separator may have a lifeof about 7 years, but with contaminants (e.g., 5 ppm Cr), the separatordeteriorates in about 6 months.

In some areas of the world, for example, Asia, lead/acid batteries aresold as ‘dry charge’ batteries. These dry charge batteries are purchasedwithout the water/acid included. The dry charge battery has a longershelf life. However, the user may not be careful to fill the batterywith uncontaminated water/acid. The contaminated water/acid will lead tooxidation of the separator and ultimately to battery failure. Thecontaminants in the water/acid may be sourced from the water/acidcontainers, e.g., steel drums.

U.S. Pat. No. 5,221,587 discloses the use of latex in the separator toprevent antimony (Sb) poisoning of the lead/acid battery. Antimonypoisoning does not cause separator oxidation; instead, antimonypoisoning causes water loss from the electrolyte. Antimony is sourcedfrom the lead plates (electrodes) of the battery. Antimony is used as analloying agent in the lead to improve the manufacture of the plates andthe cycle life of the battery. Those of ordinary skill would notconsider the teachings of U.S. Pat. No. 5,221,587 in arriving at asolution to the separator oxidation problem mentioned above.

U.S. Pat. No. 6,242,127 discloses the use of cured, porous rubber in aconventional polyolefin separator to improve the electrochemicalproperties (antimony suppression) of the separator.

SUMMARY OF THE INVENTION

A battery separator for a lead/acid battery is resistant to oxidationarising from the use of water or acid containing contaminants, forexample chromium (Cr), manganese (Mn), titanium (Ti), copper (Cu), andthe like, and combinations thereof. The separator is a microporousmembrane including a rubber. The rubber is no more than about 12% byweight of the microporous membrane. The rubber may be rubber latex, tirecrumb, and combinations thereof. The rubber may be impregnated into themicroporous membrane. The microporous membrane may be a microporoussheet of polyolefin, polyvinyl chloride, phenol-formaldehyde resins,cross-linked rubber, or synthetic nonwoven fibers. A method forpreventing the oxidation of the separator is also included.

DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings a form that is presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

FIG. 1 is a graphical comparison of the oxidation resistance, presentedas % elongation as a function of hours, of an inventive separator (B) toother known separators when the separators are subjected to a watercontaining 4.7 ppm chromium (Cr).

FIG. 2 is a graphical comparison of the oxidation resistance, presentedas % elongation as a function of hours, of an inventive separator (G) toother known separators when the separators are subjected to a watercontaining 4.5 ppm chromium (Cr).

DESCRIPTION OF THE INVENTION

Lead/acid batteries are well known, see for example, Linden, Handbook ofBatteries, 2^(nd) Edition, McGraw-Hill, Inc. New York, N.Y. (1995)and/or Besenhard, Handbook of Battery Materials, Wiley-VCH Verlag GmbHWeinheim, Germany (1999), both incorporated herein by reference. In oneembodiment, the separator, described hereinafter, may be used in alead/acid battery. The battery may be, for example, a flooded, storage,ISS, EFB, carbon, or dry charge lead acid battery with, for example,leaf, piece, pocket, or envelope type or style separators, with orwithout glass mat.

The inclusion of rubber (discussed below) with the separator of thelead/acid battery can prevent, or reduce, oxidation of the separatorcaused by contaminants, such as Cr, Mn, Ti, and the like, and therebyincrease the life cycles of batteries.

Separators, as used herein, refer to microporous membranes. Suchseparators are well known as demonstrated by reference to Besenhard,Handbook of Battery Materials, Wiley-VCH Verlag GmbH, Weinheim, Germany(1999), incorporated herein by reference. Microporous membranes may bemade from: sheets of polyolefin (e.g., polyethylene, polypropylene,ultra high molecular weight polyethylene (UHMWPE), and combinationsthereof), polyvinyl chloride (PVC), phenol-formaldehyde resins(including, for example, cellulosic and/or synthetic impregnated withphenol-formaldehyde resins), crosslinked rubber, or nonwoven (e.g.,inert fibers including cellulosic fibers or glass fibers). In oneembodiment, the microporous membranes may be made from polyethylene,UHWMPE, or a combination of both. In another embodiment, the microporousmembrane is a polyolefin (polyolefin being high molecular weight PEand/or ultra high molecular weight PE)/filler (for example a silicafiller)/processing oil, where the polyolefin/filler/processing oil aremixed and then extruded into a precursor (e.g., a flat sheet), thencalendered to create a profile (e.g., ribs) and then the processing oilis extracted therefrom. The microporous membranes may have a ribbedprofile. The ribs may be conventional, e.g., running in the machinedirection (MD) on the side to the positive electrode (e.g., to, amongother things, separate the separator from the positive electrode, andform gas channels that allow gas to escape and promotes mixing duringover charge conditions), but the ribs may also extend in the crossmachine direction (CMD) on the side to the negative electrode (to retardacid stratification).

Rubber, as used herein, refers to rubber latex, tire crumb, andcombinations thereof. In one embodiment, the rubber may beun-cross-linked or uncured rubber. In another embodiment, the rubberlatex may be natural or synthetic rubber latex. In another embodiment,the rubber may be natural rubber latex. In yet another embodiment, therubber may be tire crumb. Natural rubbers may include, for example, anygrade (e.g., latex grades), such as ribbed smoked sheet, white and palecrepes, pure blanket crepes or re-mills, thick brown crepes or ambers,and flat bark crepes. Natural rubbers may include Hevea rubbers.Synthetic rubbers may include, for example, methyl rubber,polybutadiene, chloropene rubbers, and copolymer rubbers. Copolymerrubbers may include, for example, styrene/butadiene rubbers,acrylonitrile/butadiene rubbers, ethylene/propylene rubbers (EPM andEPDM), and ethylene/vinyl acetate rubbers. Other rubbers may include,for example, butyl rubber, bromobutyl rubber, polyurethane rubber,epichlorhydrin rubber, polysulphide rubber, chlorosulphonylpolyethylene, polynorborene rubber, acrylate rubber, fluorinated rubber,isoprene rubber, and silicone rubber. These rubbers may be used alone orin various combinations.

In one embodiment, the rubber may be impregnated into the microporousmembrane. Impregnated, as used herein, means that the rubber isincorporated into the body of the microporous membrane, and is not alayer formed on the microporous membrane. So, the rubber may be mixed orblended into one or more of the materials used to form the microporousmembrane. The rubber, for example the latex, is still chemically active(i.e., uncured and/or uncross-linked) after extrusion. Thus, the rubberis a component integral with, or distributed within, or uniformlyblended throughout, or intimately blended in the materials of, themicroporous membrane.

The rubber, as described above, may comprise any portion of themicroporous membrane. In one embodiment, the rubber may comprise no morethan about 12% by weight of the microporous membrane when added to theformulation (i.e., the ‘by weight’ of the raw materials beforeextrusion). In another embodiment, the rubber may comprise about 1-12%by weight of the microporous membrane. In another embodiment, the rubbermay comprise about 1.2-6% by weight of the microporous membrane. In yetanother embodiment, the rubber may comprise about 2-4% by weight of themicroporous membrane. In still another embodiment, the rubber maycomprise about 2.5-3.5% by weight of the microporous membrane. Inanother embodiment, the rubber may comprise about 3% by weight of themicroporous membrane.

The microporous membrane may be made in any conventional fashion. Suchprocessing is well known as demonstrated by reference to Besenhard,Handbook of Battery Materials, Wiley-VCH Verlag GmbH, Weinheim, Germany(1999), incorporated herein by reference. For example, in a PE separator(microporous membrane), the rubber, for example the latex, may be mixedwith the processing oil and mixed with the PE during extrusion. Themixture is then extruded into a precursor (i.e., a flat sheet).Thereafter, the precursor is calendered to create a profile, forexample, ribs (as is conventional). Then, the processing oil isextracted from the profiled sheet, thereby creating the microporousmembrane. The microporous sheet may be subjected to further processingsteps as is conventional in the art of making separators for lead/acidbatteries.

Examples

The following is a comparison of the inventive separators (Samples B &G) to other separators. The separators are compared on basis of %elongation (a measure of embrittlement, conventional testing) versustime (hours). % elongation is measured as set forth in ASTM D882. The PEseparator refers to a conventional separator wherepolyolefin/filler/processing oil are mixed and extruded in to a flatprecursor, calendered to create the profile, and then the processing oilis extracted therefrom, as is known in the art. The difference between4.7 ppm and 4.5 ppm Cr is immaterial.

Sample Separator Comment A PE separator laminated No improvement in Crwith synthetic nonwoven oxidation resistance B PE separator with 6%Surprising improvement in by weight latex Cr oxidation resistance C PEseparator laminated No improvement in Cr with glass nonwoven oxidationresistance D PE separator highly No improvement in Cr oriented oxidationresistance E PE separator with 15% No improvement in Cr by weightresidual oxidation resistance processing oil F PE separator with Noimprovement in Cr proprietary commercial oxidation resistance(alcohol-based) additive for oxidation resistance G PE separator (35%Surprising improvement in reduction of UHMWPE Cr oxidation resistancecontent) with 6% by weight latex

The present invention may be embodied in other forms without departingfrom the spirit and the essential attributes thereof, and, accordingly,reference should be made to the appended claims, rather than to theforegoing specification, as indicating the scope of the invention.

We claim:
 1. A method of preventing or reducing separator oxidation in aflooded lead/acid battery arising from the use of water or acidcontaining contaminants comprising the steps of: providing a dry chargelead/acid battery; providing a microporous membrane within said drycharge lead/acid battery, said membrane impregnated with anuncross-linked or uncured rubber in the lead/acid battery, wherein saidmicroporous membrane comprises a microporous sheet of polyolefin,polyvinyl chloride, phenol-formaldehyde resins, cross-linked rubber, ornonwoven fibers, and adding water or acid containing contaminants, saidcontaminants including chromium, manganese, titanium, and combinationsthereof to said dry charge battery thereby flooding the battery andsubjecting the microporous membrane to said contaminants.
 2. The methodof claim 1 wherein said uncross-linked or uncured rubber comprising: nomore than about 12% by weight of the separator.
 3. The method of claim 1wherein said uncross-linked or uncured rubber comprises about 2-4% byweight of the separator.
 4. The method of claim 1 wherein saiduncross-linked or uncured rubber being selected from the groupconsisting of rubber latex, and rubber latex and tire crumb.
 5. Themethod of claim 1 wherein the contaminants further including copper incombination with the aforementioned contaminants.
 6. The method of claim1, wherein said microporous membrane comprises a sheet of polyethylene.7. The method of claim 6, wherein said microporous membrane comprises asheet of silica filled polyethylene.
 8. A method of preventing orreducing separator oxidation in a flooded lead/acid battery arising fromthe use of water or acid containing contaminants including one or moreof chromium, manganese, titanium, copper, and combinations thereofcomprising the steps of: providing a dry charge lead/acid battery;providing a microporous membrane within said dry charge lead/acidbattery, said membrane including an uncross-linked or uncured rubber inthe lead/acid battery, wherein said microporous membrane comprises amicroporous sheet of polyolefin, polyvinyl chloride, phenol-formaldehyderesins, cross-linked rubber, or nonwoven fibers, and adding water oracid containing contaminants, said contaminants including chromium,manganese, titanium, and combinations thereof to said dry charge batterythereby flooding the battery and subjecting the microporous membrane tosaid contaminants.
 9. The method of claim 8 wherein said uncross-linkedor uncured rubber being selected from the group consisting of rubberlatex, tire crumb, and combinations thereof.
 10. The method of claim 8wherein the contaminants further including copper in combination withthe aforementioned contaminants.